Island Rat Extermination Planned to Save Endangered Birds

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In an attempt to save the seabird species Henderson Petrel from
extinction on its native South Pacific island, one conservation
group is embarking on a mission to eradicate a group of
non-native rats that prey on the endangered birds.

Henderson Island is an uplifted coral island that is a part of
the United Kingdom's Pitcairn Islands. A
World Heritage Site, the island is remote and uninhabited,
with a unique array of wildlife, including large numbers of
breeding seabirds and land birds.

But although the island is mostly untouched by humans, the
presence of rats is threatening the survival of many of the
island's native species.

Unique, endangered wildlife

On Henderson Island, there are four
bird species and nine plants found nowhere else on Earth.
There are dozens of invertebrates, including eight Henderson
snails, which exist nowhere else on the planet. It is a critical
nesting site for 12 different seabird species — including four
types of petrel — as well as for marine turtles.

"Henderson Island, in the central Pacific, is one of the most
remote places on Earth. But its wildlife are not immune from
problems," said Tim Stowe, the international director of the
Royal Society for the Protection of Birds (RSPB). "Non-native
Pacific rats, which were introduced by Polynesian
settlers, have been ravaging the island’s wildlife."

The introduced Polynesian rats (Rattus exulans) are eating an
estimated 25,000 petrel chicks every year — about 95 percent of
chicks are eaten within a week of hatching — and compete with the
native birds for food. At least four species of land bird and
four of seabird have vanished from Henderson Island since the
rats' arrival.

"Once the rats are removed, we expect to be able to stand back
and watch the Henderson petrel population recover from 16,000
pairs today back up to 1.7 million pairs within 70 years," said
Jonathan Hall, a project officer with the RSPB.

Removing the rats

The operation will begin in August 2011. A team of contractors
and their equipment, including two helicopters, will be brought
in by ship.

The RSPB will be following a method pioneered in New Zealand to
clear the large islands of
bird-eating rats.

"This involves using helicopters to methodically drop poison bait
pellets across the island using GPS-guidance," Hall told
OurAmazingPlanet. "This is the only way to have a high level of
confidence of success — it would not be possible to reach all the
rats via a ground-based operation on this 14.3 square-mile (37
square-kilometer) island."

"After one complete drop, there will be a pause of 10 days, and
then the process will be repeated as a second insurance drop to
ensure that all the rats are removed," Hall added. "Over 300
islands have been successfully cleared this way, and we have
undertaken rigorous planning for the last three years, so we are
confident of success."

There are no other mammals on Henderson Island, so there is no
danger of the pellets harming anything other than the intended
target. In addition, certain bird species on the island will be
taken as a captive population for the duration of the operation
so they will not be harmed and 'scarer' measures will be put in
place on the beaches to deter shorebirds.

The RSPB will be monitoring the island again in 2013 to determine
if the project was successful. The group must wait at least two
years until any remaining rats increase to a number where they
become detectable.

"Massive long-term benefits will be achieved from this short
intervention, the whole ecosystem will benefit — the endemic land
birds, invertebrates, flora and even nesting green turtles," said
Hall. "Once the seabird population recovers, this will
re-establish the marine nutrient cycle."